(a) Field of the Invention
The present invention relates to a liquid crystal display, and more particularly, to a driving voltage generation circuit and a liquid crystal display using the same.
(b) Description of Related Art
A conventional liquid crystal display (“LCD”) includes two display panels and a liquid crystal layer having dielectric anisotropy, which is interposed between the two display panels. The LCD obtains intended image by applying electric field and controlling the intensity of the electric field to adjust the transmittance of light passing through the liquid crystal layer. The LCD is representative for portable flat panel displays (“FPDs”), and the most popular one among those LCDs is a TFT-LCD using a thin film transistor (“TFT”) as a switching element.
On a display panel on which TFTs are formed, a plurality of gate lines and data lines are formed in horizontal and vertical directions, respectively, and pixel electrodes connected to those gate lines and data lines via the TFTs are formed.
To apply image data to each pixel in such TFT-LCD, a timing controller receives image data from an image signal source (for example, computer, TV, etc.) and outputs image data to a data driver IC while outputting a driving signal to a gate driver IC in time to a prescribed timing. The gate driver IC applies a gate-on voltage, which is a scan signal, to a gate line to make the TFTs connected to the gate line turn on in order, and the data driver IC simultaneously supplies an analog signal (more specifically, a gray voltage) corresponding to the image data to each data line for the pixel line corresponding to the gate line. Then, the image signal provided to the data line is applied to each pixel via the TFT turned on. At this time, image data are applied to all pixel lines by applying gate-on voltage to all gate lines in order during one frame period to display the image of one frame.
Methods for maintaining the data voltage applied to each pixel in such LCD include an independent driving method and a previous gate driving method. The independent driving method is a method to charge the storage capacitance formed in each pixel based on the difference between the pixel voltage applied to the pixel electrode and the common voltage Vcom. The previous gate driving method is a method to charge the storage capacitance based on voltage difference between the pixel voltage applied to the pixel electrode and the gate voltage.
The previous gate driving method has advantages that amount of capacitance is larger than that of the independent driving method and that the pixel aperture ratio is larger than that of the independent driving method because separate wiring for charging storage capacitance is not required due to its panel structure. However, since the gate voltage as well as the pixel voltage and common voltage influences to the image display in the previous gate driving method, it is difficult to control the gamma curve. In addition, flicker is occurred according to the gate voltage delay due to the RC delay on the gate wiring. Moreover, the display quality becomes deteriorated due to the noise included in the voltage supplied to each pixel.